Somatic Cell Reprogramming (Part Three)

2.2. The replacement system iPS cell inducing factor and mechanism

In order to avoid the risk of tumorigenesis caused by the activation of c-Myc in i PS cells, members of the Myc family, L-Myc and N-Myc, can effectively replace c-Myc to induce human and mouse i PS cells, of which the ability of i PS cells to form chimeric mice with germline transmission can be improved, and the resulting mice do not develop tumors. The pluripotency-related factor Glis1 can also replace c-Myc to promote the reprogramming of human and mouse iPS cells, and the resulting chimeras produced by the mouse iPS cells also have the ability of germ line transmission. Glis1 promotes the induction of iPS cells by affecting a variety of reprogramming pathways, including the expression of genes Myc, Nanog, Lin28, Wnt, Essrb and the MET process.

In addition to being replaced by Klf1, Klf2 and Klf5, Klf4 can also be replaced by the orphan nuclear receptor Esrrb and the OS, two factors to achieve the induction of iPS cells. Esrrb mediates reprogramming by up-regulating pluripotent cell-specific genes. The bone morphogenetic protein Bmp4 can also replace Klf4 to promote reprogramming, and its mechanism of action is mainly to promote the MET process. Nanog and Lin28 can replace c-Myc and Klf4 to obtain human iPS cells. Nanog is one of the important factors to maintain the pluripotency of mouse embryonic stem cells. It cooperates with transcription factors such as Oct4 and Sox2 to regulate the pluripotency network, RNA binding protein Lin28 can indirectly regulate the expression of c-Myc to complete reprogramming.

Sox2 can be replaced by Sox1, Sox3, Sox15 and Sox18 of the Sox family. Rcor2 can effectively replace the exogenous Sox2 in the induction of mouse and human iPS cells, and the ogenogen factor Obox1 can replace Sox2 to obtain iPS cells. Obox1 can regulate the expression of cell cycle related genes, slow down the excessive proliferation of reprogrammed cells, and promote the MET process to promote somatic cell reprogramming. The ectoderm cell lineage specialization factor GMNN can also replace Sox2 to obtain human iPS cells. The histone variants TH2A and TH2B, which are abundantly expressed in oocytes, can replace Sox2 and c-Myc to promote the reprogramming of iPS cells. The mechanism is to enrich the X chromosome to inhibit X chromosome inactivation.

The orphan nuclear receptors Nr5a1 and Nr5a2 can replace Oct4 to induce iPS cells, respectively. The mechanism is to activate endogenous Oct4 expression. Oct4 can also be replaced by E-cadherin, the main regulator of epithelial cells. Overexpression of E-cadherin can affect the nuclear localization of β-catenin, thereby promoting the expression of pluripotency genes. In the induction of human iPS cells, the pluripotency-related factor TCL-1A can replace Oct4 and OM only to complete the reprogramming of human fibroblasts. The cells are similar and have the ability to differentiate into three germ layers. The transcription factor Brn4 can also replace Oct4 due to its homologous POU domain.

As the mechanism of each inducing factor in the induction process of iPS cells was gradually elaborated, the induction system in which the classic OSKM four factors were completely replaced also gradually appeared. Studies have shown that Sox2 can initiate the expression of pluripotency genes, including Sall4, Esrrb and Lin28, among which Sall4 can activate other pluripotency genes including Oct4. Therefore, two induction systems that completely replace OSKM are reported: Sall4, Esrrb, Lin28 and Dppa2 or Nanog composed of four factors can complete the induction of iPS cells. However, the induction efficiency of these two systems is low. The six-factor induction system that completely replaces OSKM includes Glis1, Sall4, Lrh1, Jdp2, Jhdm1b, and Id1, which can obtain iPS cells more efficiently.

2.3. The chemical induction system of iPS cells and mechanism

Since exogenous reprogramming factors are easily integrated into the cell genome, and multiple reprogramming factors are involved in the regulation of cancer-related signaling pathways, minimizing the number of transcription factors in the induction system is the first step to improve the biological safety of iPS cells. The use of small molecular compounds instead of reprogramming factors is one of the research directions for improving the safety of iPS cells and optimizing iPS cell technology. The establishment of a complete induction system using small molecule chemicals has revealed more signaling pathways and epigenetic mechanisms related to induced pluripotency.

Histone deacetylase inhibitors (HDACi) Valproic acid (VPA) can effectively replace c-Myc to complete the reprogramming of mouse fibroblasts, and can even replace c-Myc and Klf4 Reprogramming of human fibroblasts. Vitamin C can be reprogrammed with histone demethylase Jhdm1a instead of Klf4, c-Myc and Jhdm1b instead of Sox2, Klf4, c-Myc Inhibiting TGF-β signaling can activate the expression of endogenous Nanog to replace Sox2 and c-Myc. Since the activation of TGF-β plays an important role in the ME differentiation process, inhibiting TGF-β can replace Sox2 induction system. Protein methyltransferase inhibitor BIX01294 and calcium channel agonist BayK8644 can also effectively replace Sox2. Although there have been reports of many systems in which small molecule chemicals are used instead of transcription factors for induction, there has been no progress in screening small molecule compounds to replace Oct4. Using a small molecule combination system of TGF-β inhibitors, HDAC inhibitors, MEK inhibitors and phosphoinositide-dependent kinase PDK1a. Human iPS cells can be induced with a single transcription factor Oct4.

Although both SCNT and iPS cells can bring the cells to a pluripotent state, the ways to achieve pluripotency are different. iPSC technology is to reprogram cells into pluripotent cells similar to ES cells using certain transcription factors or small molecular compounds, while SCNT technology is to transfer donor cells to enucleated oocytes to achieve that donor cells are reprogrammed to a totipotent state similar to fertilized eggs.

The reprogramming speed of SCNT and iPSC technology is also very different. The SCNT reprogramming process occurs very quickly and can be completed within a few hours. The rapid histone replacement driven by egg histones may be the reason for this rapid reprogramming. In contrast, the process of iPS cell reprogramming is relatively slow, and the ectopic expression of exogenous inducing factors first causes a gradual change in cell morphology, and then the expression of pluripotency markers such as alkaline phosphatase and SSEA-1 Before the gradual increase, the expression of somatic cell-specific genes decreased. After a few days or even weeks, the stable expression of endogenous Oct4 and Nanog indicates the completion of the reprogramming process.

Reference

[1] Hupalowska A, Jedrusik A, Zhu M, Bedford M T, Glover DM, Zernicka-Goetz M. CARM1 and paraspeckles regulate preimplantation mouse embryo development. Cell 2018;175 (7) :1902-16, e13.

[2] Liu W, Liu X, Wang C, Gao Y, Gao R, Kou X, et al. Identification of key factors conquering developmental arrest of somatic cell cloned embryos by combining embryo biopsy and single-cell sequencing. Cell Discov 2016; 2:16010.

[3] Wen D, Banaszynski LA, Rosenwaks Z, Allis CD, Rafii S.H3.3replacement facilitates epigenetic reprogramming of donor nuclei in somatic cell nuclear transfer embryos. Nucleus 2014;5 (5) :369-75.

[4] Redmer T, Diecke S, Grigoryan T, Quiroga-Negreira A, Birchmeier W, Besser D.E-cadherin is crucial for embryonic stem cell pluripotency and can replace OCT4 during somatic cell reprogramming. EMBO Rep 2011;12 (7) :720-6.

Will Severe Asthma Be the Next Hot Antibody Drugs (I)?

 

About Omalizumab

Omalizumab was first FDA approved in 2003 to treat adults and children 12 years of age and older with moderate to severe persistent allergic asthma which is not controlled by inhaled steroids. Since its U.S. approval, more than 200,000 patients older than 12 with allergic asthma have been treated. In August 2017, CFDA officially approved Novartis Tall® (Omalizumab) for the treatment of moderate to severe persistent allergic asthma, which means that China’s asthma treatment has entered the era of antibody drugs. Then in September 2018, a new prefilled syringe formulation of this drug was approved by the FDA.

Omalizumab has been listed for 17 years, and in 2016 brought Novartis nearly $ 800 million in annual sales. It is estimated that there are about 340 million asthma patients in the world, and the asthma drug market is about 16 billion US dollars and will continue to grow.

The role of antibody drugs in the treatment of asthma, especially severe uncontrollable asthma, is becoming more and more important, and its market share will also increase.

Facing the complicated immune system and asthma pathology, which targets are more likely to become the next market contenders?

About Asthma

Asthma is a chronic inflammatory disease of the respiratory tract. The pathogenesis is more complicated. It is generally believed that it is caused by genetic and environmental factors. The main features of the disease are airway hypersensitivity, reversible airflow obstruction, bronchospasm muscle spasm, and airway inflammation. Common symptoms include wheezing, difficulty breathing, coughing, and chest tightness.

The 2014 Global Asthma Report shows that the incidence of asthma is about 4.3%, which means that about 334 million people worldwide have asthma of varying degrees. It is expected that by 2025, this number will increase by 100 million to 434 million.

Asthma imposes a great financial burden on society and individuals. It is estimated that the annual expenditure of asthma in advanced economies accounts for 1% to 2% of their total medical expenditure, which is higher than the sum of tuberculosis and AIDS.

The Market Share of Asthma

The treatment of asthma generally follows the step-by-step treatment guidelines of the Global Initiative for Asthma (GINA). Commonly used drugs include inhaled / oral glucocorticoids (ICS / OCS), leukotriene receptor antagonist (LTRA), long-acting β2 receptor agonist (LABA), short-acting β2 receptor agonist (SABA), Long-acting muscarinic receptor antagonist (LAMA), theophylline, etc. Antibody drugs have also been included in treatment guidelines since 2005.

Due to the large number of patients and the long course of illness, asthma drugs have always been the mainstay of respiratory system drugs. The global asthma drug market in 2022 is likely to reach US $ 22 billion.

From the perspective of drugs, long-acting β2 receptor agonists + glucocorticoid combined inhalation (LABA + ICS), or both single-use drugs dominate the market, accounting for almost half of the market. Considering that there are some ultra-long-acting β2 receptor agonists (ultra-LABA) that are used once a day in the research and development, the market position of these drugs will be further consolidated in the next five years.

LAMA occupies the second place in the market (18%). As a commonly used rapid asthma relieving agent, SABA can account for approximately 6.5% of the market. As the classic combination of LABA + ICS faces patent expiration and other issues, new combination dosage forms such as LAMA + LABA, LAMA + LABA + ICS and other new combinations run into the market to replace classic combination.

An obvious trend is the rapid rise of antibody drugs. Although there are only four asthma antibody drugs in the global market, it is certain that this proportion and market share will continue to grow rapidly. It is expected to reach 2.2 billion US dollars in 5 years.

Antibody drugs: hope for patients with severe uncontrollable asthma

Most asthma patients can be well controlled under the existing treatment guidelines, but about 5% to 10% have severe or uncontrollable asthma. However, the medical expenses of this small group of patients can account for more than 60% of the entire asthma treatment expenditure, because the deterioration rate and hospitalization rate of this part of the patients are relatively high, occupying more outpatient and emergency resources.

Individually, patients with severely uncontrollable asthma spend more than type 2 diabetes, stroke, or chronic pulmonary obstruction (COPD).

The following factors have led to the limitations of existing guidelines for the treatment of severe asthma:

First, the curative effect is limited. Patients with mild to moderate asthma can be well managed according to the guidelines, but the mortality and morbidity of severe asthma patients have not been effectively improved.

Second, adverse reactions. Inhaled drugs have good safety record, and oral drugs should be more noticeable. For example, oral glucocorticoids are more likely to cause systemic adverse reactions and potential morbidity; theophylline has a narrow therapeutic window and poor tolerance.

Third, the patient’s compliance is poor. It is estimated that approximately 50% of children and 30-70% of adults cannot strictly follow the treatment regimen of the asthma guidelines. There are many reasons for this, such as improper use of inhalants, complicated treatment plans, and patients’ concerns about adverse reactions.

Fourth, there are comorbidities. Many asthma patients have obesity, cardiovascular disease, allergies, smoking and other comorbidities, which bring more challenges to treatment. Usually, comorbidities and asthma form a vicious circle.

Because antibody drugs directly target the immune mechanism of asthma, it has brought hope to many severely uncontrollable patients. In order to better understand the targets of antibody drugs, let’s first understand the inflammatory mechanism of severe asthma.

The inflammatory response of asthma is very complicated, involving a series of immune cells and inflammatory molecules in the respiratory cavity.

Triggering of allergic asthma begins when respiratory epithelial cells secrete interleukins 25, 33 (IL-25, IL-33) and thymic stromal lymphopoietin (TSLP) after exposure to allergens, thereby activating dendritic cells (DC).

The immunogen is presented to helper T cells (Th0) after DC treatment, and the latter secretes IL-4 to activate Th2 helper cells. Th2 cells are activated to release more IL-4 and IL-13, thereby promoting B cells to produce immunoglobulin E (IgE).

IL-4 and transforming growth factor β (TGFβ) secreted by Th2 cells can also activate Th9 helper cells to secrete IL-9, thereby promoting the growth of mast cells.

Mast cells bound by IgE can bind antigens, causing the cells to degranulate and release a large amount of chemical mediators, such as histamine, prostaglandins, leukotrienes, etc., which induces the contraction of bronchial smooth muscle and further stimulates the inflammatory response. Th2 cells can also secrete IL-5 to ensure the survival and growth of eosinophils.

In addition, Th17 helper T cells are an important role in the pathogenesis of non-eosinophilic asthma, which can produce IL-17 to recruit and expand neutrophils.

To be continued in Part II…

 

The Importance of Ceramide to The Skin in Spring

The recent weather has been cold and hot. I believe that many sensitive partners have unstable skin temperature and environmental changes, which cause facial skin, allergies, redness, peeling, and even some small rashes. A bad word is Began to rotten. So how can friends with sensitive muscles prevent allergies in the more sensitive season of spring?

The formation of red blood cells is mostly caused by improper skin care, which results in too thin stratum corneum, which leads to the loss of skin barrier protective factor ceramide. If ceramide is insufficient, the barrier function is reduced, the skin cannot lock in nutrients and moisture, and it is easy to become red, hot, and dry. Frequent skin allergies. How to cure the red blood on the face, the most effective method is to replenish the ceramide lost from the skin.

The main symptoms of red blood cells are the damage to the skin barrier, and the disorder of the skin’s metabolic function makes the skin unable to operate normally. How to cure the red blood on the face, and the formation of red blood is not a matter of two or three days, but also the result of long-term accumulation.

Since you don’t want the symptoms of rotten skin, you need to base your skin. Only healthy skin can cope with the change of harsh environment, then we have to talk about this ceramide. Ceramide is naturally occurring in our skin and is a lipid. It forms a waterproof barrier on the surface of the skin and helps the skin retain moisture. It is also an important part of the stratum corneum, and plays an important role in maintaining the moisture balance of the stratum corneum. Therefore, ceramide can not only help the skin lock water, but also promote the skin barrier to repair itself and regulate skin cells. Unfortunately, as you get older, the ceramides in your skin are gradually lost.

Ceramide is a gospel for people with sensitive muscles. It can not only help thicken the stratum corneum, increase the tolerance of the entire skin, protect it from harmful substances from the outside world, avoid allergies, and repair red bloodshot blood. In addition, ceramide has a very good anti-aging, whitening and antioxidant effects. And more than one type of ceramide in our skin is formed by the reconciliation of multiple ceramides, and different ceramides have different effects.

Sufficient ceramide in the skin can resist external stimuli, like having a strong barrier. But if it is missing or not, the skin loses its natural protective effect, and it has no defense ability against all external physical and biological damage. Therefore, timely supplementation of ceramide is very imminent.

Don’t want your skin to become dry with age, lose elasticity or even have an allergic reaction, just prepare a ceramide skin care product!

Proteins Involved in DNA Repair May Contribute to the Suppression of Cancer

Every day, cells in the body undergo numerous divisions. New cells are used to replace old, damaged or dead cells. However, before a cell divides, DNA is copied first to make a precise copy and passed on to the new cell.

To start the replication process, the DNA double helix unfolds first, so that each strand can be used as a template for the synthesis of new DNA. Scientists call the stretched DNA strand fragments replication forks. As this highly complex replication process proceeds, both strands of the original DNA may break or be damaged thousands of times.

“In fact, DNA sequences suffer considerable “damage” during replication, which is why complex mechanisms are needed to ensure that the replication process is protected.”

 

Accumulating evidence suggests that the pathway for repairing DNA breaks is called homologous recombination (HR). The key factor in HR is a protein called Rad51 that binds to a single DNA strand at the broken end and supports the replication fork by transforming the fork into a structure similar to a chicken foot.

In a recent study, the authors constructed mutants of RAD51 to better understand its key function at the replication fork.

“We created a recombination-deficient variant of RAD51 that still binds DNA, but it does not search for complete copies of DNA or perform strand exchange,” said the authors. “The more we learn about this process, the more likely we are to figure out how it creates problems in cancer, and we can help improve future treatment strategies.”

In a recent study published in Nature Communications, Mason found that the strand-exchange activity of Rad51 is not required for the repair process, but that it is important to restart replication after removing the barrier.

“The field wants to understand the role of this pathway in cancer and the role of each participating factor,” Mason said.

Other scientists in the field of cancer biology could apply the RAD51 gene mutation to their own studies to help further elucidate the replication process and better understand ways to repair breaks, Mason says.

Application Value of Enzymes Creates Good Market Development Prospects

Enzymes are protein molecules that act as specific catalysts for chemical reactions. Researchers have made significant contributions to the traditional and modern chemical industries by improving existing processes. Representative industrial applications of enzymes are concentrated in the fields of technology applications, feed industry, food processing and cosmetics. Enzymes are natural catalysts. They are produced by living organisms to increase the speed of the enormous and diverse learning reactions required for life. They involve all processes necessary for life, such as DNA replication and transcription, protein synthesis, metabolism, and signal transduction. And their ability to perform very specific chemical transformations makes them increasingly useful in industrial processes.

 

Enzymes are used in a variety of applications including technical applications, food manufacturing, animal nutrition, cosmetics, pharmaceuticals, and research and development tools. Currently, nearly 4,000 enzymes are known, of which about 200 original types of microorganisms are used commercially. However, only about 20 enzymes are produced on a real industrial scale. As the understanding of enzyme production biochemistry, fermentation processes and recovery methods increases, more and more industrial enzymes can be foreseen.

 

Enzymes have great potential in agriculture, biomass processing and biofuel production. In fact, some enzymes in agriculture have brought more effectiveness than traditional chemical processes, while at the same time being less harmful to the environment. Today, more and more enzymes are being used to increase agricultural productivity, improve biofuel quality, and achieve economical biomass conversion. The use of enzymes in arable agriculture and biofuels can alleviate the pursuit of agriculture and fossil energy. Therefore, new enzyme preparations are constantly being developed.

 

As a sustainable catalyst with a high reaction rate, enzymes are more concerned than chemical catalysts. Today, more and more chemical processes are replaced by enzymes due to clean and efficient catalytic performance. For example, in chiral synthesis, the enzyme exhibits extremely high stereospecificity, which is not observed in chemical catalysts, which simplifies the overall synthesis process.

 

The beauty and fascination of enzymes for research in industrial biotechnology are well-known. The total demand for enzymes in the global market is expected to increase rapidly in recent years. Carbohydrase will remain the main enzyme in the next few years. While strong growth in product categories will be led by multiple markets, including the food and beverage, animal feed and detergent industries. The application of medicinal enzymes will grow fastest as more per capita income in developing regions leads to more people getting health care.

 

 

 

 

 

Enzymes are protein molecules that act as specific catalysts for chemical reactions. Researchers have made significant contributions to the traditional and modern chemical industries by improving existing processes. Representative industrial applications of enzymes are concentrated in the fields of technology applications, feed industry, food processing and cosmetics. Enzymes are natural catalysts. They are produced by living organisms to increase the speed of the enormous and diverse learning reactions required for life. They involve all processes necessary for life, such as DNA replication and transcription, protein synthesis, metabolism, and signal transduction. And their ability to perform very specific chemical transformations makes them increasingly useful in industrial processes.

 

Enzymes are used in a variety of applications including technical applications, food manufacturing, animal nutrition, cosmetics, pharmaceuticals, and research and development tools. Currently, nearly 4,000 enzymes are known, of which about 200 original types of microorganisms are used commercially. However, only about 20 enzymes are produced on a real industrial scale. As the understanding of enzyme production biochemistry, fermentation processes and recovery methods increases, more and more industrial enzymes can be foreseen.

 

Enzymes have great potential in agriculture, biomass processing and biofuel production. In fact, some enzymes in agriculture have brought more effectiveness than traditional chemical processes, while at the same time being less harmful to the environment. Today, more and more enzymes are being used to increase agricultural productivity, improve biofuel quality, and achieve economical biomass conversion. The use of enzymes in arable agriculture and biofuels can alleviate the pursuit of agriculture and fossil energy. Therefore, new enzyme preparations are constantly being developed.

 

As a sustainable catalyst with a high reaction rate, enzymes are more concerned than chemical catalysts. Today, more and more chemical processes are replaced by enzymes due to clean and efficient catalytic performance. For example, in chiral synthesis, the enzyme exhibits extremely high stereospecificity, which is not observed in chemical catalysts, which simplifies the overall synthesis process.

 

The beauty and fascination of enzymes for research in industrial biotechnology are well-known. The total demand for enzymes in the global market is expected to increase rapidly in recent years. Carbohydrase will remain the main enzyme in the next few years. While strong growth in product categories will be led by multiple markets, including the food and beverage, animal feed and detergent industries. The application of medicinal enzymes will grow fastest as more per capita income in developing regions leads to more people getting health care.

The Ultimate Guide to Whole Genome Resequencing: Basic and Advanced Facts (VI)

  1. Types of experimental design

With the maturity and popularity of sequencers such as Illumina’s Nova-seq, X-Ten, the price of resequencing will continue to become more and more popular. Given that resequencing is already a common research tool, the scale of competition sequencing has slowly lost value, and most of us are not mathematics / statisticians, and it is difficult to develop new algorithms. In an era where test techniques and analysis methods are similar, to stand out, it is destined to strengthen relevant biological issues and understanding of various data analysis methods, and improve experimental design and data mining interpretation capabilities.

QTL positioning (including GWAS, phenotype): in a broad sense, QTL positioning include classic linkage analysis and association analysis. The core difference between linkage analysis and association analysis in QTL positioning is that the characteristics of the studied group are different, but there is almost no statistical difference between the two analysis methods in statistics. In general, QTL mapping is a type of phenotypic identification method. We need to accurately measure the phenotype of all individuals, and then through the correlation analysis of phenotype and genotype (there are multiple models to choose from), locate the QTL related to the trait. As sequencing prices continue to fall, the core issue of QTL positioning is actually phenotyping. The accuracy of individual phenotype identification is affected by many factors, and its accuracy directly affects the effect of QTL localization. Because certain phenotypes must be performed under certain environmental conditions (for example, drought resistance must be observed under drought conditions), so individuals must be strictly controlled under similar environmental conditions for testing.

For human species, which can actively cooperate with experiments, phenotypic identification is often relatively easy. But for animal plants, accurate phenotypic identification means that this species has been domesticated. Only under the environment of artificial domestication and control of the living environment, accurate phenotype identification can become possible.

Population genetics (selection pressure analysis).

According to the research purpose and the characteristics of the experimental design, the editor mainly uses classic examples as examples to analyze the future experimental design and analysis methods.

The QTL positioning and selection pressure analysis are essentially different in experimental design (Savolainen et al. 2013) [animal and plant resequencing].

Somatic mutation.

High-depth sequencing to determine the mutation type, and then GWAS analysis, functional analysis of the contribution rate of each site. Combined with the transcriptome to express differential functional effects.

3.1 Resequencing GWAS mapping functional genes (QTL mapping (including GWAS, phenotype))

In 2017, Visscher and others reviewed the results of the whole-genome association analysis (GWAS) in the “10 Years of GWAS Discovery: Biology, Function, and Translation” in “The American Journal of HumanGenetics” in the title of The American Journal of HumanGenetics The development and application directions of the past ten years were prospected. The article points out that the results of GWAS have revealed hundreds of complex disease traits. In most studies on traits and diseases, mutation targets in the genome will appear very large. Therefore, future GWAS will be based on whole genome sequencing (Visscher et al. 2017).

Japanese researchers Yano et al. identified 26 loci (−log10 P ≥4.77) related to heading date by re-sequencing the whole genome of 176 Japanese japonica varieties and using a mixed linear model for GWAS correlation analysis The five regions of interest are located on chromosomes 1, 3, 6, 7, and 11, respectively. Among them, the peaks located on chromosomes 3 and 7 are consistent with the reported QTL mapping results of heading stage-related genes Hd6 and Hd2. The candidate region located on chromosome 1 is anchored between 36.30Mb and 36.65Mb (346Kb), including 91 loci associated with heading stage, these loci are distributed on 7 genes, of which the gene LOC_Os01g62780 and Arabidopsis. The HESO1 gene is homologous, and this gene exhibits delayed flowering in Arabidopsis. The analysis found that the valine at position 328 was mutated to isoleucine to form two haplotypes, and the varieties containing haplotype B headed Varieties that are later than haplotype A. The gene sequences of haplotype A and haplotype B were introduced into Nipponbare respectively. The flowering time of the haplotype B sequence was later than that of the haplotype A sequence and the control group, indicating that the new gene LOC_Os01g62780 and delay in rice Flowering related (Yano et al. 2016).

3.2 Population resequencing for adaptive evolution and functional gene positioning (population inheritance (selection pressure analysis))

To observe the traces of genes adapted to localization, the key factor is experimental design, especially the selection of groups. One of the key factors is whether there is migration between different groups, because localized adaptation is often associated with some degree of group isolation (whether it is artificial or natural isolation). The division of subgroups caused by geographical isolation is relatively easy to understand, for example, a high mountain blocks the possibility of migration between two subgroups.

So, how do subgroups arise from non-geographically isolated groups? In such a group, localized adaptation is the result of a balance of choice and migration. I have to mention one concept here: antagonistic pleiotropy, which seems to be more reasonable to be translated as “antagonism gene pleiotropy”. This concept actually says that in many cases, adaptation comes at a cost: that is, at the cost of loss of adaptability in other environments, a stronger local adaptability is obtained.

The significance of antagonistic pleiotropy is that the migration ability of the population is also reduced to a certain extent, thereby enhancing the localization adaptation. This also explains that the crops, livestock and poultry bred by human beings are somewhat more precious, and they are very dependent on the environment provided by human beings and have no adaptability under natural conditions. In fact, it is the cost of pursuing high yield in the process of human breeding selection. If it is not antagonistic pleiotropy, a dominant genotype is very strong in any environment, and it may slowly occupy other niche, resulting in the gradual fixation of this locus.

Most of the traits we focus on (especially the production traits of animals and plants) are related to adaptive selection. How to locate and screen these genes related to adaptive traits has been a hot spot in genomic research.

To be continued in Part VIII…

Pathogens and Food Poisoning

Researchers analyzed information from a database of people. They tracked food poisoning cases in some US laboratories, covering millions of people. The researchers found some food-borne pathogens, including bacteria, virus and parasites. Here are some details.

  1. Campylobacter

One of the most common foodborne disease bacterium is Campylobacter, which is often found in raw poultry. Campylobacter is a zoonotic disease. Wild animals, domestic animals and pets are important hosts of Campylobacter, and many countries have detected a high rate of infection in the intestines of pigs, cattle, sheep, chickens, ducks and pigeons. Infected animals usually have no obvious symptoms, but can discharge bacteria to the outside for a long time, causing human infections. In developed countries, eating raw or undercooked poultry meat is the most common cause of Campylobacter infection. The resulting cases in the United States, New Zealand and other places account for 10% -50% of the total. Due to the limited sanitary conditions in developing countries, water-borne transmission is the most common, and Campylobacter can be isolated from river, stream, mountain spring, and well water. Drinking unsterilized milk is also an important cause of infection. In addition, direct contact with infected animals and pets is often the cause of infection for slaughterhouse workers and children.

  1. Salmonella

The second most common bacterium is Salmonella, with 16 infections per 100,000 people; followed by Shigella and Escherichia coli (STEC), 4 infections per 100,000 people. Some Salmonella species are specifically pathogenic to humans, some are only pathogenic to animals, and others are both human and animals. Salmonellosis is a general term for different forms of humans, domestic animals and wild animals caused by various types of salmonella. The feces of people infected with Salmonella or carriers can contaminate food and cause food poisoning. According to statistics, among the various types of bacterial food poisoning in various countries of the world, food poisoning caused by Salmonella often ranks first.

  1. E. coli

E. coli is a normal resident bacterium in the intestines of animals, and a small part of them cause disease under certain conditions. The serotypes of E. coli can cause gastrointestinal infections in humans or animals, mainly caused by specific fimbria antigens, pathogenic toxins and other infections. In addition to gastrointestinal infections, it can also cause urinary tract infections, arthritis, and meninges Inflammation and septic infection.

  1. Staphylococcus

Staphylococcus food poisoning is mainly caused by leftover food and leftovers. It should be noted that only ingesting live bacteria with food without staphylococcal enterotoxin will not cause food poisoning, and only ingesting a poisonous dose of the enterotoxin will cause disease. Staphylococcus food poisoning has a short incubation period, generally 2-5 hours, rarely exceeding 6 hours. Sudden onset, staphylococcal food poisoning symptoms include nausea, vomiting, upper and middle abdominal pain and diarrhea, vomiting is the most significant. However, it usually recovers quickly within a few hours to 1-2 days.

  1. Botox

Botulinum toxin poisoned by botulinum is a neurological food poisoning. It is often caused by eating cured meat contaminated with botulinum, poorly prepared canned food, and edible bean paste, stinky tofu and stale fish, pork. Among the various types of food poisoning that have been reported, reports of botulism are relatively rare, but the poisoning consequences are extremely serious. The incubation period is 12-48 hours or longer, no fever, and gastrointestinal symptoms are rare. The symptoms of botulism food poisoning mainly include headache, dizziness, drooping eyelids, diplopia, dilated pupils, aphonia, dysphagia, difficulty in breathing, even respiratory paralysis and even death, the mortality rate is more than 50%.

  1. Halophiles

Halophilic bacteria are a kind of marine bacteria, so it is called halophilic bacteria, also known as vibrio parahaemolyticus. It widely lives in marine products, fish and crabs in seawater. Therefore, the source of pollution causing halophilic food poisoning is often seafood, the most common being shrimp, crab or various marine fish. The incubation period varies from 1 hour to 4 days, most of which is around 10 hours, and generally recovers faster.

The researchers concluded that “more control measures are needed” to prevent foodborne diseases, including “new or revised performance standards for meat and poultry, and strengthening training and guidance for industry and inspection personnel” etc.

The Research of Proteolytic Targeting Chimeras (I)

In recent years, cell therapy, immunotherapy and gene editing technology have developed rapidly. In the research and development of new drugs, the research of traditional small-molecule drugs is facing unprecedented challenges. The research of small molecule inhibitors urgently needs to find a new breakthrough from the mechanism of action. Traditional small molecule inhibitors work by occupying the active site or binding pocket of the target protein, thereby inhibiting the activity of the target protein and directly blocking the specific function of the target protein. Due to the limitation of the mechanism of action, small molecule inhibitors mainly have the following problems: higher drug concentrations are required to fully occupy the binding site of the target protein, and it can also lead to side effects such as off-target effects; many potential drug targets do not have clear active sites, such as backbone proteins, transcription factors, and non-enzymatic proteins. It is difficult to find corresponding high-affinity small molecule inhibitors.

To make up for the limitation that small molecule inhibitors are mainly used to regulate the activity of target proteins, researchers have begun to study how to directly regulate the expression level of proteins in the body, and have achieved many results; such as RNA interference, antisense oligonucleotides and gene editing, etc.  However, due to drug-producing, transmembrane, and clinical application reasons, such technologies need to be further improved. Proteolysis targeting chimeras (PROTACs) breaks through the mode of action of traditional small molecule inhibitors and can directly induce the degradation of substrate proteins through the ubiquitin-proteasome protein degradation pathway in vivo, which has attracted widespread attention from researchers.

Proteolysis targeting chimeras (PROTACs) are a class of compounds which can induce the poly-ubiquitination of the target proteins and promote their degradation. As a bifunctional molecule, RPOTAC has a wide range of space for application and development. PROTAC is a new direction in the field of drug discovery, and the strategy of regulating protein content in vivo by degrading target proteins greatly expands the range of potential drug targets.

Proteolytic targeting chimeras are small bifunctional molecules, one end binding to the target protein link by a chain to the other end binding to E3 ubiquitin ligase. After PROTAC enters the cell, its target protein (protein of interest (POI)) ligand specifically binds to the target protein, and the other end of the E3 ligase (E3 ligand) binds to the E3 ligase (E3 ligase). Thereby, a POI-PROTAC-E3 ligase ternary complex is formed. E3 ligase mediates the ubiquitin-binding enzyme E2 to ubiquitinate the target protein. After the ternary complex is dissociated, the target protein labeled with ubiquitin is delivered to the protease degradation in the body (proteasome), thereby selectively reducing the level of the target protein. This process does not require the target protein ligand to occupy the binding site for a long time. It only needs the short-term formation of a ternary complex to complete the ubiquitination of the target protein. The ubiquitinated protein can be recognized and degraded by the proteasome, and PROTAC can function multiple times in the cell.

Figure 1. PROTAC recruitment of an E3 ligase for target protein degradation via the ubiquitin-proteasome pathway.

Due to the lack of small molecular ligands for E3 ubiquitin ligase, the first generation of PROTAC was based on peptide motifs as ligands for E3 ubiquitin ligase. Although these molecules provide proof of concept for PROTAC, the sequences lack cellular permeability, thus limiting its use as a chemical probe. Studies have confirmed that the target proteins that can be successfully degraded by peptide PROTAC include androgen receptor (AR), methionine aminopeptidase 2 (MetAP2), and protein kinases (AKT, PI3K). These studies confirm that regulating protein half-life by targeting E3 ligase is a potential strategy for potential drug development. However, these peptides, PROTAC, have poor transmembrane absorptivity, low activity in degrading proteins, and degradation activity is still at the micromolar level.

The second generation of PROTAC is a small molecule PROTAC. The use of small molecules as part of the E3 ubiquitin ligase has enabled rapid development of small molecule-based PROTAC technology. Small molecule-based PROTAC offers many advantages over peptide-based PROTAC. Most importantly, PROTAC based on small molecules is more promising for drug development because small molecules are more easily absorbed by the body. At present, more than 600 E3 ligases have been found in the human body, but currently the only E3 ligases involved in the reported PROTAC are mouse double minute 2 homologue (MDM2), cellular inhibitor of apoptosis protein 1 (cIAP1), cereblon (CRBN), von Hippel-Lindau (VHL)etc., mainly due to the lack of small molecule ligands with high affinity and specific E3 ligase.

Recruiting E3 ubiquitin ligase MDM2

In 2008, Vassilev et al. used Nutlin-3a as a ligand for the E3 ubiquitin ligase MDM2. The PROTAC is a linker between Nutlin-3a and a non-steroidal androgen receptor (AR) ligand via a polyethylene glycol chain.

Figure 2. Recruiting MDM2’s small-molecule PROTAC

Recruiting E3 ubiquitin ligase cIAP1

cIAP1 is an intrinsic inhibitor of apoptosis. Itoh et al. used cIAP1 inhibitor aprotinin b (bestatin) as the E3 ligase recognition group, and designed and synthesized a small molecule PROTAC that targets the degradation of intracellular retinoic acid binding protein Ⅱ (CABP-Ⅱ). This molecule can induce 75% CABP-Ⅱ degradation in cancer cells at 10 μmol·L-1. Studies have shown that such small molecules PROTAC have the following limitations: 1) Because bestatin is an aminopeptidase inhibitor, it often accompanies off-target effects and causes adverse reactions. 2) Due to the lower activity of degraded proteins, higher concentrations are required to exert pharmacological effects. 3) IAP ligands often induce IAP ubiquitination and are then degraded. For these reasons, further development of bestatin as an E3 ubiquitin ligase ligand has been limited.

Figure 3. Recruiting cIAP1’s small-molecule PROTAC

Recruiting E3 ubiquitin ligase CRBN

In recent years, thalidomide and its derivatives lenalidomide and po-malidomide have attracted great interest from researchers as potent immunomodulators. A recent study found that thalidomide combined with E3 ligase CRBN can lead to the degradation of IKZF1 and IKZF3, indicating that thalidomide and its derivatives can be introduced into the design of PROTAC as an E3 ligase recognition moiety.

To be continued in Part II…

What is chemokines and more

 

Chemokines: A class of small cytokines or signaling proteins secreted by cells. Because they have the ability to induce directed chemotaxis of nearby reactive cells, they are named chemotactic cytokines.

 

Brief introduction

When the human body defends and removes foreign bodies such as invading pathogens, it has a function of directing chemotactic immune cells, and some substances can cause this function called chemokines or chemokines,

Also called chemokine, chemokine or chemical hormone. Chemokines are a family of small-molecule cytokine proteins. These small proteins are named for their ability to direct cellular chemotaxis. Some of these proteins have other names in the history of chemokines, including the SIS cytokine family, the SIG cytokine family, the SYC cytokine family, and the platelet factor-4 family.

 

Common structural features of chemokine proteins include small molecular weight (approximately 8-10 kDa) and four conserved cysteine residues to ensure their tertiary structure.

Some chemokines are considered to be pro-inflammatory cytokines and can induce cells of the immune system to enter the site of infection during the immune response. Some chemokines are believed to maintain the body’s self-regulation and control cell migration during normal tissue maintenance or development. Chemokines are present in all vertebrates, some viruses and some bacteria, but have not been found in other invertebrates.

Chemokines are divided into four main subfamilies: CXC, CC, CX3C, and XC. All these proteins exert their biological effects by interacting with transmembrane receptors (called chemokine receptors) linked to the G protein. These proteins bind to chemokine receptors. Chemokine receptors are G protein-coupled transmembrane receptors are selectively expressed on the surface of target cells.

 

Structure

All chemokines are small, with molecular weights between 8 and 10 kDa. About 20-50% of them are identical; that is, they have the same gene sequence and amino acid sequence homology. They also possess conservative amino acids, which are important for forming their three-dimensional or tertiary structure. For example, in most cases, four cysteines interact to form a Greek key shape, which is a chemokine feature. Intramolecular disulfide bonds usually connect the first to third cysteine residues, and the second to fourth cysteine residues, which are numbered when they appear in the protein sequence of the chemokine. A typical chemokine protein is produced in the form of a peptide precursor, and during its secretion from the cell, a signal peptide of approximately 20 amino acids is cleaved from the active (mature) part of the molecule. In chemokines, the first two cysteines are near the n-terminus of the mature protein, the third cysteine is in the molecular center, and the fourth is near the C-terminus. After the first two cysteines, there is a loop of about 10 amino acids, called the N loop.

 

Features

The main role of chemokines is to induce directional migration of cells. Cells attracted by chemokines migrate to the source of chemokines along the signal of increased concentration of chemokines. Some chemokines control the chemotaxis of immune cells during immune surveillance, such as inducing lymphocytes to lymph nodes. The chemokines in these lymph nodes monitor the invasion of pathogens by interacting with antigen presenting cells in these tissues. These are called steady-state chemokines and are produced and secreted without stimulating the source cells.Some chemokines play a role in development; they can stimulate new blood vessel formation (angiogenesis); guide cells into tissues and provide specific signals for cell maturation. The key role of other chemokines in inflammatory response can be released by a variety of cells in response to bacterial and viral infections; it can also be released due to non-infectious stimuli such as silica inhalation and urinary tract stones. Chemokine release is usually caused by stimulation of inflammatory cytokines such as interleukin-1 (IL-1). The main role of inflammatory chemokines is to act as a chemotactic agent for leukocytes, attracting monocytes, neutrophils and other effector cells from the blood to the site of infection or tissue damage. Certain inflammatory chemokines can activate cells to initiate an immune response or promote wound healing. They are released by many different cell types and guide the cells of the natural and adaptive immune systems.

 

The main function of chemokines is to manage the migration (homing) of leukocytes to their respective locations during inflammation and homeostasis.

Basal homing effect: Basal steady-state chemokine produced in thymus and lymphoid tissue. The chemokines CCL19 and CCL21 (expressed in lymph nodes and lymphatic endothelial cells) and their receptor CCR7 (expressed in cells destined to home to these organs) are the most stable functions of their homes in homing Good illustration. The use of these ligands allows antigen-presenting cells (APCs) to transfer to lymph nodes during an adaptive immune response. Other homeostatic chemokine receptors include: CCR9, CCR10, and CXCR5, which are important for tissue-specific leukocyte homing as part of the cell address. CCR9 supports leukocyte migration into the intestine, CCR10 supports skin migration, and CXCR5 supports b cell migration to lymph node follicles. CXCL12 (SDF-1) produced in bone marrow promotes the proliferation of B progenitor cells in the bone marrow microenvironment.

Inflammation homing: inflammatory chemokines produce high concentrations during infection or injury and determine the migration of inflammatory leukocytes to the damaged area. Typical inflammatory chemokines include: CCL2, CCL3 and CCL5, CXCL1, CXCL2 and CXCL8. A typical example is CXCL-8, which is a neutrophil chemoattractant. Compared with steady-state chemokine receptors, there is a clear confusion between binding receptors and inflammatory chemokines. This often complicates research on receptor-specific therapies

 

Types

Structural classification

Chemokines can be divided into four subfamilies of CXC, CC, C, and CX3C according to the arrangement of their amino-terminal (N-terminal) cysteine:

CC chemokine subfamily: CCL1, CCL2, CCL3, CCL4, CCL5, CCL6, CCL7, CCL8, CCL9, CCL10, CCL11, CCL12, CCL13, CCL14, CCL15, CCL16, CCL17, CCL18, CCL19, CCL20, CCL21, CCL22 , CCL23, CCL24, CCL25, CCL26, CCL27, CCL28

CXC chemokine subfamily: CXCL1, CXCL2, CXCL3, CXCL4, CXCL5, CXCL6, CXCL7, CXCL8, CXCL9, CXCL10, CXCL11, CXCL12, CXCL13, CXCL14, CXCL15, CXCL16, CXCL17

C chemokine subfamily: XCL1, XCL2

CX3C chemokine subfamily: CX3CL1

 

Functional classification

Chemokines are divided into two categories according to their functions:

Balance chemokine in the body: produced in certain tissues, responsible for the migration of basic leukocytes. Including: CCL14, CCL19, CCL20, CCL21, CCL25, CCL27, CXCL12 and CXCL13. (This classification is not strict, for example: CCL20 can also be used as a pro-inflammatory chemokine)

Pro-inflammatory chemokines: formed under pathological conditions (under pro-inflammatory stimuli, such as IL-1, TNF-α, LPS, or viruses), and actively participate in the inflammatory response, attracting immune cells to the site of inflammation. For example: CXCL-8, CCL2, CCL3, CCL4, CCL5, CCL11, CXCL10.

 

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The history and preparation method of metal powder

Metal powder refers to a group of metal particles with a size of less than 1 mm. Including single metal powder, alloy powder and certain refractory compound powder with metallic properties, it is the main raw material of powder metallurgy.

The elemental metal is generally silver-white. When the metal is under certain conditions, it is a black powder. Most metal powders are black.

Historical traceability

The preparation and application of metal powder have a long history. In ancient times, gold, silver, copper, bronze and some oxide powders were used as paints for coloring and decoration of pottery, jewelry and other utensils. In the early 20th century, American Coolidge (W.D. Coolidge) used hydrogen reduction tungsten oxide to produce tungsten powder to produce tungsten wire, which was the beginning of modern metal powder production. Since then, a variety of powders such as copper, cobalt, nickel, iron, and tungsten carbide have been prepared by chemical reduction, which has promoted the development of early powder metallurgy products (oily porous bearings, porous filters, cemented carbide, etc.); The carbonyl method is used to prepare iron powder and nickel powder. In the 1930s, the iron powder was first produced by the vortex grinding method, and then the iron powder was produced by the solid carbon reduction method at a low cost. In the early 1930s, the molten metal atomization method also appeared. This method was originally used to produce low melting point metals such as tin, lead, aluminum and other powders. In the early 1940s, it developed into iron powder produced by high-pressure air atomization. In the 1950s, high pressure water atomization was used to produce alloy steel and various alloy powders. In the 1960s, various atomization methods were developed to produce high-alloy powders, which promoted the development of high-performance powder metallurgy products. Since the 1970s, a variety of gas-phase and liquid-phase physicochemical reaction methods have emerged to produce coated powders and ultrafine powders with important uses.

Powder properties

Metal powder is a loose substance, its performance comprehensively reflects the nature of the metal itself and the characteristics of individual particles and the characteristics of the particle group. Generally, the properties of metal powders are divided into chemical properties, physical properties and technological properties. Chemical properties refer to metal content and impurity content. Physical properties include the average particle size and particle size distribution of the powder, the specific surface and true density of the powder, the shape, surface morphology and internal microstructure of the particles. Process performance is a comprehensive performance, including powder fluidity, bulk density, tap density, compressibility, formability and sintered size changes. In addition, for some special applications, the powder is required to have other chemical and physical properties, such as catalytic performance, electrochemical activity, corrosion resistance, electromagnetic performance, internal friction coefficient, etc. The performance of metal powder depends to a large extent on the production method of powder and its preparation process. The basic properties of the powder can be determined by specific standard testing methods. There are many methods for measuring the particle size and distribution of powder. Generally, sieve analysis method (> 44μm), sedimentation analysis method (0.5 100μm), gas permeation method, microscope method, etc. Ultrafine powder (<0.5μm) was measured by electron microscope and X-ray small angle scattering method. Metal powders are conventionally divided into five grades: coarse powder, medium powder, fine powder, fine powder and superfine powder.

Preparation method

Generally, it is divided into mechanical method and physical chemical method according to the principle of transformation. It can be directly refined from solid, liquid and gaseous metals, and can also be converted from metal compounds in different states through reduction, pyrolysis, electrolysis Made. Carbides, nitrides, borides, and silicides of refractory metals can generally be prepared directly by compounding or reducing-combining methods. Due to different preparation methods, the shape, structure and particle size of the same powder often vary greatly (Figure 2). The preparation method of the powder is listed as follows. Among them, the most widely used are reduction method, atomization method and electrolysis method.

Reduction method

Using a reducing agent to seize the oxygen in the metal oxide powder, the metal is reduced to a powder. Gas reducing agents include hydrogen, ammonia, coal gas, and converted natural gas. Solid reducing agents include carbon and metals such as sodium, calcium, and magnesium. Hydrogen or ammonia reduction, commonly used to produce tungsten, molybdenum, iron, copper, nickel, cobalt and other metal powders. Carbon reduction is commonly used to produce iron powder. With strong metal reducing agents sodium, magnesium, calcium, etc., tantalum, niobium, titanium, zirconium, vanadium, beryllium, thorium, uranium and other metal powders can be produced (see metal thermal reduction) Nickel, copper, cobalt and their alloys or coated powders can be prepared by reducing metal salt aqueous solutions with high-pressure hydrogen (see hydrometallurgy). The powder particles produced by the reduction method are mostly irregular shapes of sponge structure. The particle size of the powder mainly depends on factors such as reduction temperature, time and the particle size of the raw material. The reduction method can produce most metal powders and is a widely used method.

Atomization

The molten metal is atomized into fine droplets and solidified into powder in the cooling medium (Figure 3). Figure 4 The widely used two-stream (melt flow and high-speed fluid medium) atomization method is to use high-pressure air, nitrogen, argon, etc. (gas atomization) and high-pressure water (water atomization) as the jet medium to crush the metal liquid stream. There are also centrifugal atomization methods that use rotary disk crushing and the melt itself (consumable electrodes and crucibles) to rotate, as well as other atomization methods such as hydrogen-dissolved vacuum atomization and ultrasonic atomization. Due to the small droplets and good heat exchange conditions, the condensation speed of the droplets can generally reach 100 ~ 10000K / s, which is several orders of magnitude higher than when casting ingots. Therefore, the composition of the alloy is uniform and the structure is fine. The alloy material made of it has no macrosegregation and excellent performance. Aerosolized powders are generally nearly spherical, and water atomization can produce irregular shapes. The characteristics of the powder such as particle size, shape and crystalline structure mainly depend on the properties of the melt (viscosity, surface tension, superheat) and atomization process parameters (such as melt flow diameter, nozzle structure, pressure of the spray medium, flow rate, etc.). Almost all metals that can be melted can be produced by the atomization method, especially suitable for the production of alloy powders. This method has high production efficiency and is easy to expand industrial scale. It is not only used for mass production of industrial iron, copper, aluminum powder and various alloy powders, but also used to produce high purity (O2 <100ppm) high temperature alloy, high speed steel, stainless steel and titanium alloy powder. In addition, the rapid cooling powder (condensation speed> 100,000K / s) produced by the quenching technology has been paid more and more attention. It can be used to produce high-performance microcrystalline materials (see fast-cooling microcrystalline alloys).

Electrolytic method

Direct current is applied to the metal salt aqueous solution, and metal ions are discharged on the cathode to form a deposit layer that is easily broken into powder. Metal ions generally originate from the dissolution of the same metal anode, and migrate from the anode to the cathode under the action of current. The factors affecting the particle size of the powder are mainly the composition of the electrolyte and the electrolysis conditions (see electrolysis of aqueous solution). Generally, the electrolytic powder is mostly in the form of dendrites with high purity, but this method consumes a large amount of electricity and has a high cost. The application of electrolytic method is also very extensive, commonly used to produce copper, nickel, iron, silver, tin, lead, chromium, manganese and other metal powders; alloy powder can also be prepared under certain conditions. For rare refractory metals such as tantalum, niobium, titanium, zirconium, beryllium, thorium, and uranium, composite molten salts are often used as electrolytes (see molten salt electrolysis) to prepare powders.

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